scholarly journals Power and Thermal Efficiency Optimization of an Irreversible Steady-Flow Lenoir Cycle

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 425
Author(s):  
Ruibo Wang ◽  
Yanlin Ge ◽  
Lingen Chen ◽  
Huijun Feng ◽  
Zhixiang Wu
Keyword(s):  
Steady Flow ◽  
Power Output ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Cold Side ◽  
Heat Conductance ◽  
Efficiency Increase ◽  
Optimal Values ◽  
Internal Irreversibility ◽  
Conductance Distribution

Using finite time thermodynamic theory, an irreversible steady-flow Lenoir cycle model is established, and expressions of power output and thermal efficiency for the model are derived. Through numerical calculations, with the different fixed total heat conductances (UT) of two heat exchangers, the maximum powers (Pmax), the maximum thermal efficiencies (ηmax), and the corresponding optimal heat conductance distribution ratios (uLP(opt)) and (uLη(opt)) are obtained. The effects of the internal irreversibility are analyzed. The results show that, when the heat conductances of the hot- and cold-side heat exchangers are constants, the corresponding power output and thermal efficiency are constant values. When the heat source temperature ratio (τ) and the effectivenesses of the heat exchangers increase, the corresponding power output and thermal efficiency increase. When the heat conductance distributions are the optimal values, the characteristic relationships of P-uL and η-uL are parabolic-like ones. When UT is given, with the increase in τ, the Pmax, ηmax, uLP(opt), and uLη(opt) increase. When τ is given, with the increase in UT, Pmax and ηmax increase, while uLP(opt) and uLη(opt) decrease.

Power Density Optimization for an Irreversible Closed Brayton Cycle

2001 ◽  
Vol 08 (03) ◽  
pp. 241-260 ◽  
Author(s):  
Lingen Chen ◽  
Junlin Zheng ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Power Density ◽  
Heat Exchangers ◽  
Pressure Ratio ◽  
Maximum Power ◽  
Brayton Cycle ◽  
Maximum Power Density ◽  
Cold Side ◽  
Heat Conductance ◽  
Optimum Heat ◽  
Conductance Distribution

In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as objective for performance optimization of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The maximum power density optimization is performed by searching the optimum heat conductance distribution corresponding to the optimum power density of the hot- and cold- side heat exchangers for the fixed heat exchanger inventory. The influence of some design parameters on the optimum heat conductance distribution, the maximum power density, and the optimum pressure ratio corresponding to the maximum power density are provided. The power plant design with optimization leads to a higher efficiency and smaller size including the compressor, turbine, and the hot- and cold-side heat exchangers.

Cooling Load Density Optimization of an Irreversible Simple Brayton Refrigerator

2002 ◽  
Vol 09 (04) ◽  
pp. 325-337 ◽  
Author(s):  
Shengbing Zhou ◽  
Lingen Chen ◽  
Fengrui Sun ◽  
Chih Wu
Keyword(s):  
Heat Exchangers ◽  
Pressure Ratio ◽  
Design Parameters ◽  
Working Fluid ◽  
Cooling Load ◽  
Temperature Ratio ◽  
Cold Side ◽  
Optimum Pressure ◽  
Heat Conductance ◽  
Numerical Examples

The performance optimization of an irreversible simple Brayton refrigerator coupled to constant-temperature heat reservoirs is carried out by taking the cooling load density, i.e., the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective using finite-time thermodynamics (FTT) or entropy generation minimization (EGM) in this paper. The analytical formulae about the relations between cooling load density and pressure ratio, as well as between coefficient of performance (COP) and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers, and the irreversible compression and expansion losses in the compressor and expander. The influences of the effectiveness of the heat exchangers, the temperature ratio of the reservoirs, and the efficiencies of the compressor and expander on the cooling load density versus COP are provided by numerical examples. The cooling load density optimization is performed by searching the optimum pressure ratio of the compressor, and searching the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for the fixed total heat exchanger inventory. The influences of some design parameters, including the effectiveness of the heat exchangers between the working fluid and heat reservoirs, the efficiencies of compressor and expander, the temperature ratio of heat reservoirs, on the maximum cooling load density, the optimum heat conductance distribution and the optimum pressure ratio are provided by numerical examples. The refrigeration plant design with optimization leads to a smaller size including the compressor, expander, and the hot- and cold-side heat exchangers.

Maximum Attainable Performance of Stirling Engines and Refrigerators

2003 ◽  
Vol 125 (5) ◽  
pp. 911-915 ◽  
Author(s):  
P. C. T. de Boer
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Power Dissipation ◽  
Coefficient Of Performance ◽  
Cold Side ◽  
Stirling Engines ◽  
Compression And Expansion ◽  
Linearized Theory ◽  
Flow Through ◽  
Stirling Refrigerator

The flow through the regenerator of a Stirling engine is driven by differences of pressure in the compression and expansion spaces. These differences lead to power dissipation in the regenerator. Using linearized theory, it is shown that this dissipation severely limits the maximum attainable thermal efficiency and nondimensional power output. The maximum attainable values are independent of the value of the regenerator conductance. For optimized nondimensional power output, the thermal efficiency equals only half the Carnot value. The power dissipated in the regenerator is removed as part of the heat withdrawn at the regenerator’s cold side. Analogous results are presented for the Stirling refrigerator. At optimized nondimensional rate of refrigeration, its coefficient of performance is less than half the Carnot value.

Efficiency Optimizations of an Irreversible Brayton Heat Engine

1998 ◽  
Vol 120 (2) ◽  
pp. 143-148 ◽  
Author(s):  
C.-Y. Cheng ◽  
C.-K. Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Heat Engine ◽  
Thermal Conductance ◽  
Working Fluid ◽  
Reservoir Temperature ◽  
Temperature Ratio ◽  
Conductance Ratio ◽  
Internal Irreversibility

A steady-flow approach for finite-time thermodynamics is used to calculate the maximum thermal efficiency, its corresponding power output, adiabatic temperature ratio, and thermal-conductance ratio of heat transfer equipment of a closed Brayton heat engine. The physical model considers three types of irreversibilities: finite thermal conductance between the working fluid and the reservoirs, heat leaks between the reservoirs, and internal irreversibility inside the closed Brayton heat engine. The effects of heat leaks, hot-cold reservoir temperature ratios, turbine and compressor isentropic efficiencies, and total conductances of heat exchangers on the maximum thermal efficiency and its corresponding parameters are studied. The optimum conductance ratio could be found to effectively use the heat transfer equipment, and this ratio is increased as the component efficiencies and total conductances of heat exchangers are increased, and always less than or equal to 0.5.

Thermodynamic Investigation of an Irreversible Combined Stirling-organic Rankine Cycle for Maximum Power Output Condition

2021 ◽  
Author(s):  
Siddharth Ramachandran ◽  
Naveen Kumar ◽  
Mallina Venkata Timmaraju
Keyword(s):  
Heat Source ◽  
Output Power ◽  
Power Output ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Heat Recovery ◽  
Maximum Output Power ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Maximum Output

Abstract A pragmatic approach is adopted to investigate irreversible thermodynamic combined cycle devices. The finite-time thermodynamic model of combined Stirling-organic Rankine cycle is formulated and evaluated for maximum output power and thermal efficiency. The influence of effectiveness of heat exchangers, heat capacitance of external fluids, and, inlet temperatures of heat exchangers at heat source, heat recovery unit and heat sink on the performance of Stirling-organic Rankine cycle are investigated to get their corresponding optimum. The maximum allowable heat capacitance of external fluids of heat source and heat recovery units are about 1.1 kW/K and 1.4 KW/K, respectively for the operating conditions considered in the present study. The maximum power output is achieved only when the effectiveness of heat exchangers is ideal. The overall performance of Stirling-organic Rankine cycle combination will be higher than either of the performances of individual cycles provided that the isothermal heat rejection from Stirling cycle takes place at temperature above 540 K. Further, a 0.2 increase in the internal irreversibility parameter from an ideal/reversible condition reduced the maximum output power and the corresponding thermal efficiency of Stirling-organic Rankine cycle by 16.1 kW and 24%, respectively.

Optimal Allocation of Heat Transfer Area for a Heat Engine

2005 ◽  
Vol 21 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Y. C. Hsieh ◽  
J. S. Chiou
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Optimal Allocation ◽  
Heat Engine ◽  
Thermal Conductance ◽  
Heat Transfer Area ◽  
Internal Irreversibility ◽  
Optimal Area ◽  
Special Case

AbstractFor an endoreversible heat engine operates steadily between two fixed temperatures, Bejan found the engine's best performance can be obtained if the total thermal conductance is evenly divided for hot-end and cold-end heat exchangers. In this study, a heat by-pass model is used to represent the losses due to internal irreversibilities, and the more general formulations are derived for both the optimal area allocation and the maximum thermal efficiency. The results calculated from the present formulations when there is no internal irreversibility(a special case) are consistant with that obtained by Bejan.

scholarly journals Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 536
Author(s):  
Lingen Chen ◽  
Zewei Meng ◽  
Yanlin Ge ◽  
Feng Wu
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Combined Cycle ◽  
Quantum Gases ◽  
Carnot Cycle ◽  
Leakage Loss ◽  
Optimal Power ◽  
Heat Leakage ◽  
Working Medium ◽  
Ideal Quantum

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

The Effect of Baffles in Shell and Tube Heat Exchangers

2009 ◽  
Vol 62-64 ◽  
pp. 694-699 ◽  
Author(s):  
E. Akpabio ◽  
I.O. Oboh ◽  
E.O. Aluyor
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Proper Position ◽  
Process Industries ◽  
Overall Heat Transfer Coefficient ◽  
Shell And Tube ◽  
Optimal Values ◽  
Side Flow

Shell and tube heat exchangers in their various construction modifications are probably the most widespread and commonly used basic heat exchanger configuration in the process industries. There are many modifications of the basic configuration which can be used to solve special problems. Baffles serve two functions: Most importantly, they support the tubes in the proper position during assembly and operation and prevent vibration of the tubes caused by flow-induced eddies, and secondly, they guide the shell-side flow back and forth across the tube field, increasing the velocity and the heat transfer coefficient. The objective of this paper is to find the baffle spacing at fixed baffle cut that will give us the optimal values for the overall heat transfer coefficient. To do this Microsoft Excel 2003 package was employed. The results obtained from previous studies showed that to obtain optimal values for the overall heat transfer coefficient for the shell and tube heat exchangers a baffle cut of 20 to 25 percent of the diameter is common and the maximum spacing depends on how much support the tubes need. This was used to validate the results obtained from this study.

Performance Comparison and Parametric Analysis of sCO2 Power Cycles Configurations

2018 ◽  
Author(s):  
Ali S. Alsagri ◽  
Andrew Chiasson ◽  
Ahmad Aljabr
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Performance Comparison ◽  
Specific Power ◽  
Brayton Cycle ◽  
Computationally Efficient ◽  
Power Cycles ◽  
Optimization Study ◽  
Specific Power Output ◽  
Improve Calculation

A thermodynamic analysis and optimization of four supercritical CO2 Brayton cycles were conducted in this study in order to improve calculation accuracy; the feasibility of the cycles; and compare the cycles’ design points. In particular, the overall thermal efficiency and the power output are the main targets in the optimization study. With respect to improving the accuracy of the analytical model, a computationally efficient technique using constant conductance (UA) to represent heat exchanger performances is executed. Four Brayton cycles involved in this compression analysis, simple recaptured, recompression, pre-compression, and split expansion. The four cycle configurations were thermodynamically modeled and optimized based on a genetic algorithm (GA) using an Engineering Equation Solver (EES) software. Results show that at any operating condition under 600 °C inlet turbine temperature, the recompression sCO2 Brayton cycle achieves the highest thermal efficiency. Also, the findings show that the simple recuperated cycle has the highest specific power output in spite of its simplicity.

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